Method for operating a communication network and communication network

ABSTRACT

A method for operating a communication network comprising a master and a number of subscribers. A message comprising a data field is transmitted by the master, wherein at least one of the subscribers, on receiving the message, reads data out of the data field of the message, and forwards the message to at least one other one of the subscribers after the readout, and wherein the at least one other one of the subscribers, on receiving the message, writes data into the data field.

CROSS-REFERENCE TO RELATED APPLICATION

The application claims priority to German Patent Application DE 10 2014105 207.2, filed 11 Apr. 2014, entitled VERFAHREN ZUM BETREIBEN EINESKOMMUNIKATIONSNETZWERKS UND KOMMUNIKATIONSNETZWERK, which isincorporated by reference herein, in the entirety and for all purposes.

FIELD

The invention relates to a method for operating a communication networkcomprising a number of subscribers. The invention further relates to acommunication network.

BACKGROUND

In order to implement acyclic communication in an Ethernet network, forexample in an EtherCAT network according to IEC Standard “IEC 61158” insuch a manner that the cyclic real-time communication is not disturbed,there are usually two options. In option 1, a master controls thecomplete acyclic communication, that is to say that the acyclic messageswhich must be transmitted from a slave to the master, are also fetchedfrom the master (for example in an EtherCAT communication network knownfrom the prior art). In the second option, phases are specified in whichacyclic communication is allowed to take place (for example in aPROFINET IRT communication network also known from the prior art). Inoption 1, the line cannot be used in both directions during thetransmission of the acyclic messages since either an acyclic message istransmitted to the slave (write, the returning message is withoutcontent in this case), or read by the slave (read, the incoming messageis unused in this case). In option 2, overload situations can easilyoccur since a number of slaves have to send messages at the same time.In addition, the configuration of the various phases is complex.

In cyclic communication, the data transmission is performed initerative, equally long time intervals, the cycles. Cyclic communicationoccurs usually in each cycle again and again in the same manner, forexample for the exchange of process data (inputs/outputs) but also forstatus monitoring. The exchanged volume of data between individualsubscribers is in each case rather low; as a rule, real-timerequirements are present.

Acyclic communication, as a rule, does not occur in each cycle butusually only as required. On the other hand, the volume of data isfrequently greater than in the case of process data; the transmissionhas no or only few real-time requirements. The greater volume of datamust frequently be transmitted in relatively small units between thecyclic data in order not to impair their real-time requirements.

SUMMARY

The present invention provides an improved method for operating acommunication network comprising a number of subscribers.

The present invention provides an improved communication network.

According to one aspect, for operating a communication networkcomprising a master and a number of subscribers, a message comprising adata field is transmitted by the master, wherein at least one of thesubscribers, on receiving the message, reads data out of the data fieldof the message, and forwards the message to at least one other one ofthe subscribers after the readout, and wherein the at least one otherone of the subscribers, on receiving the message, writes data into thedata field.

According to another aspect, a communication network comprises a masterand a number of subscribers, the master and the subscribers beingconnected to one another via a data line. The master comprises atransmit interface to the data line by means of which the master sends amessage to the subscribers and a receive interface to the data line bymeans of which the master receives the message from the subscribersafter passing through the subscribers. The message comprises a datafield. At least one of the subscribers, on receiving the message, readsdata out of the data field of the message and forwards the message afterthe readout to at least one other one of the subscribers, wherein the atleast one other one of the subscribers, on receiving the message, writesdata into the data field of the message.

According to another aspect, for operating a communication networkcomprising a master and a number of subscribers, the master transmits amessage to the subscribers, the message comprising a data field and atleast two address fields associated with a data field, one address fieldindicating a first subscriber which is to read data out from the datafield and the other address field indicating second subscriber which isto write data into the data field, wherein the second subscriber beinglocated downstream of the first subscriber with respect to a runningdirection of the message.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 shows an EtherCAT message.

FIG. 2 shows an EtherCAT message with a data field.

FIG. 3 shows a communication network.

FIG. 4 shows a further communication network.

FIG. 5 shows a flow chart of a method for operating a communicationnetwork.

DETAILED DESCRIPTION

In the following, reference is made to embodiments of the invention.However, it should be understood that the invention is not limited tospecific described embodiments. Instead, any combination of thefollowing features and elements, whether related to differentembodiments or not, is contemplated to implement and practice theinvention. Furthermore, in various embodiments the invention providesnumerous advantages over the prior art. However, although embodiments ofthe invention may achieve advantages over other possible solutionsand/or over the prior art, whether or not a particular advantage isachieved by a given embodiment is not limiting of the invention. Thus,the following aspects, features, embodiments and advantages are merelyillustrative and are not considered elements or limitations of theappended claims except where explicitly recited in a claim(s). Likewise,reference to “the invention” shall not be construed as a generalizationof any inventive subject matter disclosed herein and shall not beconsidered to be an element or limitation of the appended claims exceptwhere explicitly recited in a claim(s).

In the text which follows, identical reference symbols can be used foridentical features.

FIG. 1 shows an EtherCAT message 101.

The EtherCAT message 101 comprises an Ethernet head section 103, alsocalled Ethernet header. Furthermore, the EtherCAT message 101 comprisesa number of datagrams 105. Two datagrams are shown explicitly. Thereference symbol 107 points to a box of the EtherCAT message 101 inwhich five points are drawn. This is intended to show symbolically that,instead of the box 107, further datagrams 105 can be provided.

The datagrams 105 in each case comprise a datagram head section 109,also called datagram header. The datagram head section 109 comprises adestination address (i.e. an address field with a destination address ofa subscriber) of a subscriber of a communication network, wherein thedatagram 105 having the datagram head section 109 corresponding to thedestination address is intended. Furthermore, the datagram head section109 comprises a command or a number of commands which the subscriberhaving the destination address is to execute.

Furthermore, the datagrams 105 comprise in each case data 111 for thesubscriber having the corresponding destination address. Furthermore,the datagrams 105 comprise in each case a counter 113, also calledworking counter, which indicates whether processing of the correspondingdatagram 105 by means of the subscriber having the correspondingdestination address was successful. It is preferably possible to addressone or a number of subscribers by means of each datagram 105.

The EtherCAT message 101 comprises also a checksum 115 which can beformed, for example, over the data 111. The checksum 115 can be, forexample, a CRC (Cyclic Redundancy Check) checksum.

FIG. 2 shows a further EtherCAT message 201.

Analogously to the EtherCAT message 101 of FIG. 1, the EtherCAT message201 comprises an Ethernet head section 103. The curved bracket with thereference symbol 203 comprises or points to a datagram 205 of theEtherCAT message 201. The curved bracket with the reference symbol 207comprises or points to a datagram head section 209 or datagram header ofthe datagram 205. The datagram head section 209 comprises a commandfield 211, a first address field 213 and a second address field 215. Thedatagram 205 comprises also a data field 217 into which data can bewritten and out of which data can be read. In this context, the firstaddress field 213 comprises an address of a first subscriber of anEtherCAT communication network, which is to read data out of the datafield 217. The second address field 215 comprises an address of a secondsubscriber of the EtherCAT communication network which is to write datainto the data field 217. The command field 211 comprises a command whichorders the first subscriber to read data out of the data field 217 andwhich orders the second subscriber to write data into the data field217. The command can be, for example, an FMRW command. “FMRW” stands forthe terms: Fixed address Multiple Read Write. In this context, it ispreferably provided that the first subscriber reads the data out of thedata field 217 so that the data field 217 is empty after the reading ofthe data. The second subscriber thus writes data into an empty datafield 217. The message 201 also comprises a checksum 115 which, inparticular, can be formed over the data in the data field 217. Thechecksum 115 can be, for example, a CRC checksum 115. The order of theindividual elements (address field and command field) or components ofthe datagram head section 209 can be, for example, arbitrary and doesnot necessarily have to correspond to the order shown in FIG. 2. Thisorder shown is only exemplary but not restrictive. This also applies tothe datagram head section 109 of FIG. 1. The command in the commandfield 211 can be, for example, a read, write or read/write command or anarbitrary combination thereof, in each case with different addressingtypes, that is to say with addresses which subscriber is to executewhich command.

Furthermore, the datagram 205 comprises a counter 113, that is to say aworking counter which indicates whether a write process into a readprocess from the data field 217 has been carried out successfully. Forthis purpose, it is preferably provided that the counter 113 isincremented after a successful write process and after a successful readprocess. In particular, in the case of only one counter 113, the counter113 is incremented with different increments in dependence on whetherwriting into the data field 217 or reading out of the data field 217 wassuccessful.

In an embodiment, two counters 113 can be provided, one of the twocounters being incremented exclusively in the case of a successful writeprocess into the data field 217 and the other counter being incrementedexclusively in the case of a successful read process out of the datafield 217.

In an embodiment, the EtherCAT message 201 can also have datagrams 105analogously to FIG. 1 in addition to the datagram 205. This means, inparticular, that the EtherCAT message 101 of FIG. 1 can be extended witha datagram 205 of FIG. 2. In particular, it can be provided that adatagram head section 109 of FIG. 1 according to datagram head section209 of FIG. 2 is formed.

FIG. 3 shows a communication network 301.

The communication network 301 comprises a number of subscribers 303which are designed to perform the method according to the invention.Four subscribers 303 a,b,c,d are shown. However, two, three or more thanfour subscribers 303 a,b,c,d can be provided. The communication network301 comprises a further subscriber 305 which is configured as master.The four subscribers 303 a,b,c,d are configured as slaves. The master305 and subscribers 303 a,b,c,d are connected to one another via a dataline 311.

The master 305 has a transmit interface 307 by means of which the master305 can send messages to the subscribers 303 a,b,c,d. Such a message canbe, for example, the message 101 of FIG. 1 or the message 201 of FIG. 2.The master 305 comprises a receive interface 309 by means of which themaster 305 can receive messages from the subscribers 303 a,b,c,d. Thetransmission of a message via the communication network 301 can beperformed, for example, as follows.

The master 305 sends the message 201 (the statements apply analogouslyto message 101) via its transmit interface 307 to the one of thesubscribers 303 which directly follows the master 305 via the data line311, in this case subscriber 303 a. A running direction of the message201 sent out is shown with an arrow having the reference symbol 313. Themessage 201 then runs successively in the running direction from left toright through the four subscribers 303 a,b,c,d. After running throughthe fourth subscriber, in this case subscriber 303 d, the message 201 issent back to the master 305 by the last one of the four subscribers,that is to say subscriber 303 d. The master receives the message 201 viaits receive interface 309.

The first address field 213 of datagram 205 can contain, for example,the address of subscriber 303 b. The second address field 215 ofdatagram 205 can contain, for example, the address of subscriber 303 d.The master 305 can preferably perform this addressing. The master 305can, for example, write data into the data field 217. When the message201 is transmitted via the communication network 301, that is to saywhen the message 201 runs through subscribers 303 a,b,c,d, the message201 is received by a subscriber 303 b. Subscriber 303 b reads the dataout of the data field 217 so that the data field 217 is empty after thereadout. For example, the data field 217 has a logical zero. Thesubscriber 303 b forwards the message 201 to subscriber 303 c. Thelatter forwards the message 201 to subscriber 303 d. Subscriber 303 dwrites data into the data field 217 and subsequently forwards themessage 201 to the master 305. The master 305 receives the message 201via its receiving interface 309.

In the communication network 301 of FIG. 3, a section 311 a of the dataline 311 which leads from the last subscriber 303 d back to the master305 no longer runs through the four subscribers 303 a,b,c,d. A dataexchange is thus possible only in one direction, the running direction.In this embodiment, the subscriber which is to read data out of the datafield 217 must therefore be arranged before the subscriber which is towrite data into the data field 217, with relation to the runningdirection. However, this applies only under the premise that data are tobe written into an empty data field 217. If a logical combination of thedata to be written with data already present in the data field 217 isprovided, a position of the subscribers which are intended to write andof the subscribers which are intended to read can be mutually arbitrary.

The four subscribers 303 a,b,c,d also have in each case a transmitinterface for transmitting and a receive interface for receivingmessages.

FIG. 4 shows a further communication network 401.

The communication network 401 is essentially structured analogously tothe communication network 301 of FIG. 3. Reference is made to thecorresponding statements. As a difference, section 311 a of the dataline 311, which leads from the last subscriber 303 d back to the master305, runs through the four subscribers 303 a,b,c,d on its return path. Adata exchange is thus possible both on a forward path of the message 201from the transmit interface 307 of the master 305 through thesubscribers 303 a,b,c,d and on a return path from the last subscriber303 d through the four subscribers 303 a,b,c,d to the receive interface309 of the master 305. In this configuration, a positioning of thesubscriber which is to read with respect to the subscriber which is towrite is therefore arbitrary. This is independent of whether it isintended to write into an empty data field 217 or whether a logicalcombination between data to be written and data already present in thedata field 217 is intended.

Thus, for example, the subscriber which is to read data out of the datafield 217 can be the subscriber 303 d. The subscriber which is to writedata into the data field 217 can be, for example, subscriber 303 a.Transmission of the message 201 via the communication network 401 canthen be as follows.

The master 305 sends out the message 201 via its transmit interface 307.In the first address field 213 of the datagram 205, the address of thesubscriber 303 d is located. In the second address field 215 of thedatagram 205, the address of subscriber 303 a is located. In data field217, data are located which the subscriber 303 d is intended to read.The message 201 successively runs through subscribers 303 a,b,c,d. Whensubscriber 303 d receives the message 201, it reads the data out of thedata field 217. This may be empty, for example after the readout, andtherefore for example have a logical zero. The message 201 then runs viasection 311 a of the data line 311 again through subscriber 303 d, thensubscriber 303 c, then subscriber 303 b and is then received bysubscriber 303 a. Subscriber 303 a writes data into the data field 217and subsequently sends the message 201 to the master 305 which receivesthe message 201 by means of its receive interface 309.

FIG. 5 shows a flow chart of a method for operating a communicationnetwork which comprises a number of subscribers.

According to a step 501, a message comprising a data field is receivedby a first subscriber. The message can be formed, for example,analogously to the message 201 of FIG. 2. In a step 503, the firstsubscriber reads data out of the data field so that the data field isempty after the reading. According to step 505, the first subscriber,after the readout, forwards the message with the empty data field. In astep 507, the message with the empty data field is received by a secondsubscriber which writes data into the empty data field according to step509. In one embodiment, it may be provided that after the writing, thesecond subscriber sends the message to a further subscriber or to amaster. The second subscriber can follow the first subscriber directly,for example. Preferably, further subscribers are arranged between thefirst and the second subscriber so that the message must firstly runthrough these further subscribers before it reaches the secondsubscriber.

In an embodiment, the method can also be used for a slave-to-slavecommunication or in that reading is done by a subscriber and writing iscarried out into a subscriber through which the message (frame) runslater.

In one embodiment, the method can be extended in order to provide for aso-called “one-to-many communication.” In this embodiment, reading iscarried out by a subscriber and writing is performed with several or allfollowing subscribers. For this purpose, the datagram head section(datagram header) 209 is extended by corresponding identifiers. Thedatagram head section 209 thus has a corresponding identifier. Forexample, the identifier or the identification can be a broadcast flagand/or a group address.

In one embodiment, it may be provided that data are read by a number ofsubscribers, the respective data to be read being written in each caseinto the data field and during this process being logically combinedwith the data already present in the data field, wherein these logicallycombined data can be written preferably into a further subscriber. Thefurther subscriber thus reads out the logically combined data. Thelogical combination can be effected, for example, by ORing the data inthe data field 217 of the message 201 with the data to be read out ofthe subscribers (i.e. the data which are to be written into the datafield 217). In principle, for example, other logical and/or arithmeticoperations can also be performed or used as logical combination.

According to one aspect, a method for operating a communication networkcomprising a number of subscribers is provided, wherein a messagecomprising a data field is transmitted via the communication network,wherein at least one of the subscribers, on receiving the message, readsdata out of the data field of the message, forwards them after thereadout and wherein at least one other one of the subscribers, onreceiving the message, writes data into the data field.

According to another aspect, a communication network is providedcomprising a number of subscribers which are configured to perform themethod for operating a communication network.

According to another aspect, a computer program is provided whichcomprises a program code for performing the method for operating acommunication network when the computer program is executed on acomputer, for example a subscriber.

A common data field in a message is provided in which subscribers of thecommunication network can both write data and can read data out of thedata field. By this means, in particular, an efficient utilization ofthe data field is advantageously provided. This is because in thismanner, for example, the subscribers can exchange data with one anotherby means of the data field. Thus, a subscriber can write data into thedata field which are read out by another subscriber. Thus, a common datafield is advantageously available to the subscribers for an exchange ofdata. The message can thus be used always independently of whether it issent by a master which, in particular, is also a subscriber to thecommunication network, to the subscribers, that is to say the slaves, orwhether it is sent from the slave to the master. The message can alwaysbe used. This is in contrast to the known prior art in which, independence on a write or read access of the subscribers, the messageremains unused either on the way from the master or on the way back tothe master.

In one embodiment, it can be provided that the message has a number ofaddress fields with associated addresses of the subscribers which are toread data out of the data field or write data into the data field. Inparticular, this causes the technical effect that it is known whichsubscriber is to read data out of the data field and which subscriber isto write data into the data field. Thus, each subscriber knows when itis receiving the message, whether it is to write data into the datafield or read data out of the data field. In particular, this thus meansthat the address fields have an identifier, for example a flag, whichindicates whether the subscriber to which the address of the addressfield is allocated, is to read data out of the data field or write datainto the data field. In particular, an address field can comprise abroadcast flag and/or a group address which indicates that the messageis to be processed (reading of data out of the data field and/or writingof data into the data field) by the subscribers which are comprised oraddressed by the group address or the broadcast flag.

In a further embodiment, it can be provided that the message has atleast one counter which is incremented on reading out of and/or writinginto the data field. This produces, for example, the technical effectthat a log is kept about a successful read process and/or about asuccessful write process so that it is also possible subsequently at anytime to determine how many write processes and/or read processes arecarried out. Such a counter can be designated as a “working counter.”The counter is incremented, in particular, only if the read processand/or the write process have been carried out successfully. The counterfor read processes, in particular, can be designated as a read counter.The counter for write processes can be designated, for example, as awrite counter. If only one counter is provided, it can be designated, inparticular, as a read/write counter.

According to a further embodiment, it can be provided that the messagehas two counters, one counter being incremented exclusively duringreading out of the data field and the outer counter being incrementedexclusively during the writing into the data field. This produces thetechnical effect, for example, that an even more accurate log aboutsuccessful write processes and/or read processes can be kept which canbe read out in a particularly simple manner. This is because, due to thetwo counters, the information is available directly on how many writeprocesses and how many read processes have been carried out.

According to another embodiment, it can be provided that incrementing iscarried out with different increments depending on whether reading orwriting is performed. In particular, this produces the technicaladvantage that, for example, only one counter is needed. This isbecause, from the count, it is possible to calculate back due to thedifferent increments how many write processes and how many readprocesses have been carried out. In the case of two counters, inparticular, the technical effect is produced that specifying the countalone is sufficient for determining whether the corresponding counter isthe counter for write processes or the counter for read processes. Thecounter (read counter or read/write counter) is thus incremented by afirst increment in a read process. In a write process, the counter(write counter or read/write counter) is incremented by a secondincrement. The first increment and the second increment are different.

In a further embodiment, it can be provided that when writing data intothe data field, the data to be written are logically combined with dataalready present in the data field. This produces, for example, thetechnical effect that further data can be written into the data fieldalthough there are already data present in the data field. Combining cancomprise, for example, ORing of the data to be written with the dataalready present. In particular, the combining can also comprise otherlogical and/or arithmetic operations and/or arbitrary combinationsbetween logical and arithmetic operations between the data to be writtenand the data already present. The logical operation can comprise, forexample, a logical AND in order to determine, for example,advantageously whether all subscribers are in the same state. Thearithmetic operation can comprise, for example, an arithmetic SUM inorder to, for example, advantageously contrast or combine counters,particularly error counters, to form a total count, particularly a totalerror count.

According to another embodiment, respectively, it can be provided that

-   -   the message is received by a first subscriber,    -   which reads data out of the data field so that the data field is        empty after the reading, wherein    -   the first subscriber, after the readout, forwards the message        with the empty data field wherein    -   the message with the empty data field is received by a second        subscriber which writes data into the empty data field.

In particular, this produces the technical effect that by means of onemessage, a read process can be performed efficiently at one subscriberand a write process at a second subscriber, which does not require anyconfiguration of phases in which acyclic communication is provided, andthat the master can decide with each resending of the message whichsubscribers of the communication network it wishes to address. Due tothe empty data field, the entire storage space is available to thesecond subscriber for writing data into the data field. Since in thecase of an empty data field, no combining of data to be written withdata already present needs to be carried out, a processing time and acomputing effort are thus reduced. The message can thus be forwardedadvantageously, after the writing of the data into the data field,rapidly and with less delay relative to a processing comprising acombination. In the sense of the present invention, “empty” can mean,for example, that the data field has no content. “Empty” in the sense ofthe present invention, can mean, for example, that the data field has alogical zero (0) as the only content.

According to one embodiment, it can be provided that a master sends themessage to a subscriber, particularly the first subscriber or the secondsubscriber.

In one embodiment, it can be provided that the subscribers forward areceived message to the next subscriber.

In a further embodiment, it can be provided that the subscriber,particularly the first subscriber or the second subscriber, sends themessage to a further subscriber, particularly the second subscriber orthe first subscriber.

In another embodiment, it can be provided that the subscriber,particularly the first subscriber or the second subscriber, sends themessage to the master.

If, according to one embodiment, a data exchange with a message betweenthe subscribers can take place or be performed only in one direction(for example a forward or a reverse direction; forward direction orforward path is the direction from the master to the subscriber, reversedirection or a return path is the direction from the subscriber to themaster), it is provided in particular that a subscriber (for example thefirst subscriber) which is to read data out of the data field, islocated before the subscriber (for example the second subscriber), withrelation to a direction of data exchange or a running direction of themessage, which is to write data into the data field. This is because ifno combining is to be performed, the data field must first be emptybefore data can be written into the data field again. Thus, the datamust first be read out of the data field by means of a subscriber (forexample first subscriber) before data can be written into the data fieldby a further subscriber (for example second subscriber). In thisembodiment, a data line from the subscriber back to the master no longerruns through the subscribers so that they can no longer receive andprocess the message on the return path of the message.

If, according to one embodiment, a data exchange can take place or beperformed with the message between the subscribers in both directions(that is to say forward and reverse direction), it can be provided inparticular that a positioning of a subscriber (for example the firstsubscriber) which is to read, and of a subscriber (for example thesecond subscriber) which is to write is arbitrary. In this way, thereading of the data out of the data field can be performed in theforward direction or on the forward path, that is to say the directionfrom the master in the direction of the subscriber. Writing data intothe data field can be performed on the reverse direction or on thereturn path, that is to say the direction from the last subscriber ofthe communication network back to the master. In this embodiment, a dataline runs from the subscriber back to the master via the subscribers sothat the latter can receive and process the message on the return pathof the message.

According to one embodiment, it can be provided that the subscribers aresubscribers to an automation system or an automation facility. Theautomation system or facility can comprise, for example, a controlsystem and/or control facility. The subscribers can be preferablysubscribers of a control system and/or of a control facility. Thismeans, therefore, that the corresponding system and/or facilitymentioned above has a number of subscribers which are connected to oneanother via a communication network. For example, a data line connectsthe subscribers to one another. For example, the data line connects themaster to the subscribers. Via the communication network, messages canbe transmitted so that messages can be forwarded from one subscriber tothe next subscriber.

According to one embodiment, the communication network is an Ethernetcommunication network. The message can be, for example, an Ethernetmessage.

According to another embodiment, the communication network is anEtherCAT communication network. The message can be, for example, anEtherCAT message.

The message can comprise, for example, a datagram, wherein the datagramcan comprise the aforementioned counter or the aforementioned countersand/or the data field and/or the aforementioned address fields. Themessage can be formed, for example, analogously to the message 201 ofFIG. 2 as will still be explained in the text which follows.

According to another embodiment, subscribers can control and/or read outan actuator and/or a sensor, this particularly being based on a receivedmessage, particularly being based on data of the data field. This means,therefore, in particular, that a subscriber can control and/or read outan actuator and/or a sensor, this being based on a received message,particularly being based on data of the data field. Thus, for example, asubscriber can write data into the data field which comprise informationon a status of the actuator and/or of the sensor. Thus, for example, asubscriber can read data out of the data field which compriseinformation on how the subscriber is to control the actuator and/or thesensor.

When the subscriber reads data out of the data field, these data readout are preferably written into the subscriber, particularly into amemory of the subscriber and/or of the associated actuator and/orsensor. Thus, reading data out of the data field produces, inparticular, writing data into the subscriber, that is to say a writeaccess of the subscriber.

When the subscriber writes data into the data field, these data to bewritten are read out of the subscriber, in particular, particularly outof a memory of the subscriber and/or of the associated actuator and/orsensor. Writing data into the data field thus produces, in particular,reading data out of the subscriber, that is to say read access of thesubscriber.

According to one embodiment, a subscriber can process a receivedmessage. Processing can comprise, for example, reading data out of themessage, particularly out of the data field. Processing can comprise,for example, writing data into the message, particularly into the datafield. The subscriber can, for example, forward the processed message.

According to one embodiment, it can be provided that a subscriber onlyforwards a received message, that is to say does not process it.

According to one embodiment, the communication network can have atopology selected from the following group of topologies: ring, line,star, tree and a combination thereof

The statements made in conjunction with the method apply analogously tosubscribers and to the communication network and conversely. Inparticular, this means that embodiments with regard to a subscriberand/or a communication network can result from embodiments with regardto the method and conversely in each possible combination. If thesingular is used for “subscriber,” the plural should always be read alsoand conversely.

1. A method for operating a communication network comprising a masterand a number of subscribers, wherein a message comprising a data fieldis transmitted by the master, wherein at least one of the subscribers,on receiving the message, reads data out of the data field of themessage, and forwards the message to at least one other one of thesubscribers after the readout, and wherein the at least one other one ofthe subscribers, on receiving the message, writes data into the datafield.
 2. The method as claimed in claim 1, wherein the message has anumber of address fields, one of the address fields indicating thesubscriber which is to read data out of the data field and another oneof the address fields indicating the subscriber of the data field whichis to write data into the data field.
 3. The method as claimed in claim1, wherein the message has at least one counter which is incremented onat least one of reading out and writing into the data field.
 4. Themethod as claimed in claim 3, wherein incrementing is carried out withdifferent increments depending on whether reading or writing isperformed.
 5. The method as claimed in claim 1, wherein the message hastwo counters, wherein one counter is incremented exclusively on readingout of the data field and the other counter is incremented exclusivelyon writing into the data field.
 6. The method as claimed in claim 1,wherein during a writing of data into the data field, the data to bewritten are logically combined with data already present in the datafield.
 7. The method as claimed in claim 1, wherein a first subscriberreads data out of the data field of the message so that the data fieldis empty after the reading, wherein the first subscriber, after thereadout, forwards the message with the empty data field, and wherein themessage with the empty data field is received by a second subscriberwhich writes data into the empty data field.
 8. A communication networkcomprising a master and a number of subscribers, the master and thesubscribers being connected to one another via a data line, the mastercomprising a transmit interface to the data line by means of which themaster sends a message to the subscribers and a receive interface to thedata line by means of which the master receives the message from thesubscribers after passing through the subscribers, the messagecomprising a data field wherein at least one of the subscribers, onreceiving the message, reads data out of the data field of the messageand forwards the message after the readout to at least one other one ofthe subscribers and wherein the at least one other one of thesubscribers, on receiving the message, writes data into the data fieldof the message.
 9. The communication network as claimed in claim 8,wherein the message has a number of address fields, one of the addressfields indicating the subscriber which is to read data out of the datafield and another one of the address fields indicating the subscriber ofthe data field which is to write data into the data field.
 10. Thecommunication network as claimed in claim 8, wherein the message has atleast one counter which is incremented on at least one of reading outand writing into the data field.
 11. The communication network asclaimed in claim 10, wherein incrementing is carried out with differentincrements depending on whether reading or writing is performed.
 12. Thecommunication network as claimed in claim 8, wherein the message has twocounters, wherein one counter is incremented exclusively on reading outof the data field and the other counter is incremented exclusively onwriting into the data field.
 13. The communication network as claimed inclaim 8, wherein during a writing of data into the data field, the datato be written are logically combined with data already present in thedata field.
 14. The communication network as claimed in claim 8, whereina first subscriber reads data out of the data field of the message sothat the data field is empty after the reading, wherein the firstsubscriber, after the readout, forwards the message with the empty datafield, and wherein the message with the empty data field is received bya second subscriber which writes data into the empty data field.
 15. Amethod for operating a communication network comprising a master and anumber of subscribers, wherein the master transmits a message to thesubscribers, the message comprising a data field and at least twoaddress fields associated with a data field, one address fieldindicating a first subscriber which is to read data out from the datafield and the other address field indicating second subscriber which isto write data into the data field, wherein the second subscriber beinglocated downstream of the first subscriber with respect to a runningdirection of the message.
 16. The method as claimed in claim 15, whereinthe message has at least one counter which is incremented on reading outand on writing into the data field, wherein incrementing is carried outwith different increments depending on whether reading or writing isperformed.
 17. The method as claimed in claim 15, wherein the messagehas two counters, wherein one counter is incremented exclusively onreading out of the data field and the other counter is incrementedexclusively on writing into the data field.
 18. The method as claimed inclaim 15, wherein during a writing of data into the data field, the datato be written are logically combined with data already present in thedata field.
 19. The method as claimed in claim 15, wherein the firstsubscriber reads data out of the data field of the message so that thedata field is empty after the reading, wherein the first subscriber,after the readout, forwards the message with the empty data field, andwherein the message with the empty data field is received by the secondsubscriber which writes data into the empty data field.